kohler tub spout replacement help!

I've searched internet/youtube and felt confident I was ready to tackle replacing the tub spout/diverter. When I pulled spout off pipe....white plastic was on it with what also looks like an o ring. How do I get this off? It doesn't pull easily but does spin easily....do I have to figure out what it is and replace that then a new spout or can I just "push on" and tighten down the allen nut on the new spout? I'm including a picture on what I see on the pipe....